Machines for moving materials such as earth and stones, included among which are excavators and the like, and other machines used in public works and mining, are used to pull out, move and load earth and stones. These machines, which can be presented with a variety of configurations, are usually provided with one or more buckets joined to a mechanical arm. The bucket is provided with a beveled lip or blade on a front edge intended for striking against and penetrating the earth and stone mass. It is common to assemble wear members or teeth associated to the blade and projecting forwardly therefrom to prevent excessive wear of the blade and to aid in penetrating the earth. However, said blades are also subjected to wear and breaks, whereby they must often be replaced, and on the other hand, depending on the work which the machine is to perform, it may be desirable to change the type or shape of the teeth. To facilitate said replacement, wear member and adaptor member, tooth and tooth bar, assemblies are used in which the tooth bars are fixed to the blade of the bucket in a more or less permanent manner and the teeth are releasably coupled to the tooth bar by means of respective interlocking configurations. The coupling is held together by means of at least one pin or other retainer member.
There are different types of coupling systems between teeth and tooth bars, it being common in most of them that upon applying a downward vertical force on the front part of the tip of the tooth, reactive forces are generated due to the structure of the coupling that are contrary to the direction of the coupling between tooth and tooth bar. That is, forces are generated which tend to “decouple” both members, considerably increasing stresses both on the surface of the tooth bar and in the pin securing the interlocking between both members.
In traditional interlocking systems between a wear piece and an adaptor member thereof, or a tooth and tooth bar, the housing in the tooth and the nose of the tooth bar have a wedge shape. This shape creates stresses when a downward vertical force is applied (usual manner of the work of the machine) on the tip of the tooth which tend to separate the tooth from the tooth bar, subjecting the pin retaining both members to great stress (see FIG. 9a).
Patent document U.S. Pat. No. 4,761,900 discloses a tooth and tooth bar assembly for an excavator in which a slightly arched pin is used to hold the coupling between the tooth and tooth bar and a retainer member is used to lock the pin.
The pin used has a rectangular cross section with rounded corners and has two opposite planar faces and two opposite arched faces of different radii, such that the cross section area decreases from a middle area towards the ends. About halfway between the ends of one of the planar faces there is a cavity for housing said retainer member, which is joined to a plate from which there is projected towards the opposite part a rod surrounded by a compressed coil spring, which is supported on said plate at one end and joined to a base disc at the other end. The spring is embedded in an elastomeric material forming a cylinder between the plate and base disc, constituting a retractable and at the same time dust, dirt and moisture resistant one-piece body. The one-piece body is housed in a cavity opening into a wall of the tooth bar such that in the absence of stresses, the retainer member projects from said wall. As the pin is introduced in a passage defined in collaboration by respective configurations of the tooth and tooth bar when they are coupled together, a beveled end of the pin acts like a cam on the head of the retainer member such that the retractable body is shortened and the retainer member is hidden, allowing the passage of the pin. When said cavity of the pin reaches a position ahead of the retainer member, the latter penetrates therein, pushed by the resilient force of the spring holding the pin in place.
One drawback of the device of this patent U.S. Pat. No. 4,761,900 is that the insertion of the pin must be carried out by means of hammering to achieve the shortening of the retainer member against the force of the spring and the tightening of the wider cross section middle area of the pin. Although the retainer member has a cone-shaped tip cooperating with inclined walls of the housing of the pin, hammering must be used also for the removal of the tooth in order to achieve the shortening of the retainer member. In a general sense, hammering is usually imprecise with respect to force and direction and can damage or weaken members of the tooth, tooth bar, pin and/or retainer member, therefore an assembly device not requiring hammering for carrying it out is desirable.
In order for the pin to be retained in the tooth-tooth bar coupling system in this retention system, the pin is supported in the tooth and tooth bar, such that it is essential that there not be any allowance between the tooth and tooth bar so that the pin is held in place, a retainer member further being necessary. Even though the allowance between new parts is non-existent, as teeth are changed in the tooth bar the allowance becomes greater since, in spite of the tooth being new, the tooth bar has become deformed due to the work of the previous, replaced teeth. As this allowance increases, the retainer member looses effectiveness since the tension exerted on the pin decreases, whereby the risk of loosing the pin and accordingly the wear member or tooth exists.
Patent document U.S. Pat. No. 5,983,534 discloses a lock system for a fixing pin of the coupling between a tooth and tooth bar which is rotary and does not require hammering.
In the described system, the pin incorporates a resiliently loaded member able to exert a force against one portion of the tooth or tooth bar for the purpose of tightening the socket coupling between both, and a resiliently loaded retainer member radially projecting from a cylindrical wall of the pin and susceptible to being introduced in a cavity of the tooth or tooth bar when the pin, once inserted, is rotated a predetermined angle by means of the coupling of a tool in suitable configuration provided on an axial end of the pin. A notch allows the introduction of the retainer member when the pin is axially inserted into a passage defined in collaboration by respective configurations of the tooth and tooth bar when they are both coupled. When the pin is inserted, a sloped surface acts as a cam to push the retainer member inwardly of the pin as the latter is rotated until reaching the angular position of said cavity, where the retainer member is shot into the cavity due to the effect of said resilient loading. The removal thereof is provided for by either breaking of the retainer member due to the action of striking with a hammer on the pin in the axial direction or the collaboration of inclined surfaces of the housing with corresponding inclined surfaces of the head of the retainer member to push the retainer member inwardly, either by an axial force exerted on the pin, or by a turning torque applied thereto.
This arrangement entails great complexity for the pin, since it incorporates two moving parts housed and retained in respective cavities of the body of the pin and resiliently loaded by means of coil springs, which negatively affects its production cost. On the other hand, said cavities existing in the pin for the housing of the moving parts weaken the pin. Furthermore, the moving parts and resilient springs housed in the pin are highly susceptible to being affected by the accumulation of dust and earth, which combined with moisture can form a clay-type paste which may lock the springs and the movement possibilities of the moving parts when it dries, which entails the need to destroy them by hammering when it is necessary to remove the teeth. Another drawback resides in that the use of the pressure of the resiliently loaded member against the tooth bar for holding the pin in place allows a certain relative movement between the tooth and tooth bar. As a result, the retainer is exposed to the movements of the tooth and, accordingly, the retainer may become deformed.